It has long been known that algae, nuisance invertebrates, microorganisms, and inorganic salts may foul water systems and lead to very significant water system inefficiencies. These inefficiencies result in increased energy consumption and increased maintenance demands that, in turn, increase overall operational and maintenance costs by several orders of magnitude. Ion generators have been employed in previous attempts to control algae, nuisance invertebrates, and microorganisms. Such ion generators are based on well-known principles of electrochemical reactions, one of which is referred to as electrolysis.
Electrolysis is an electrochemical process by which electrical energy is used to promote chemical reactions that occur on the surface of functionally cooperating electrodes. One electrode, called the anode, involves the oxidation process where chemical species lose electrons. A second electrode, called the cathode, involves the reduction process where electrons are gained. In water, for example, oxygen is generated at the anode and hydrogen is generated at the cathode. The generation of hydrogen and oxygen in fresh water by the process of electrolysis will be weak due to the low electrical conductivity of the water. The oxygen generated aids in the prevention of the deposit of inorganic salts on the electrodes. The function of an ion generator is also to produce metal ions, typically copper ions or silver ions. Metal ion production is accomplished by use of an electrically charged metal anode that comprises atoms of the metal ions that are to be generated. It is the purpose of the ion generator to feed the metal ions out of the generator before they can be deposited on a cathode. The metal ions and oxygen, both of which are produced by the ion generator, are fed into the water stream of the water system to prevent fouling of the system by algae, nuisance invertebrates, microorganisms, and inorganic salts. As previously mentioned, one such system was devised by these inventors and is the subject of U.S. Pat. No. 6,350,385 issued to Holt, et al.
The toxicity of copper and silver to aquatic organisms is well established although the exact mechanism is not well defined. In general, these heavy metals must be in an ionic form in order for them to be toxic to invertebrates, microorganisms and algae. The eradication of microorganisms is attributed to positively charged ions that are both surface active and microbiocidal. These ions attach themselves to the negatively charged bacterial cell wall of the microorganism and destroy cell wall permeability. This action, coupled with protein denaturation, induces cell lysis and eventual death. One advantage to the use of metal ionization is that eradication efficacy is wholly unaffected by water temperature. Chlorine, a commonly used antifouling chemical, is somewhat temperature dependent. Furthermore, the metal ions actually kill the microorganisms, and other microorganism promoting bacteria and protozoa, rather than merely suppress them, as in the case of chlorine. This minimizes the possibility of later recolonization. Other advantages of metal ionization compared to other eradication techniques include relatively low cost, straightforward installation, easy maintenance, and the presence of residual disinfectant throughout the system.
A copper or silver ion generator is, by way of specific example, an effective method for controlling legionella which is likely to be present in most water systems. Legionella is predominantly present in water cooling systems in microbial biofilms which become attached to surfaces submerged in the aquatic environment. These biofilms are typically found on the surfaces of pipes and stagnant areas of the water cooling system. Many components of most any man-made water system can be considered to be an amplifier for the organism (i.e., the organism can find a niche where it can grow to higher levels, or be amplified) or a disseminator of the organism. Examples of man-made amplifiers include cooling towers and evaporative condensers, humidifiers, potable water heaters and holding tanks, and conduits containing stagnant water. Showerheads, faucet aerators, and whirlpool baths may serve as amplifiers as well as disseminators. Human infection from exposure to legionella, or legionosis, can result in a pneumonia illness that is commonly referred to as Legionnaire's disease, namesake of the famous 1976 outbreak in Philadelphia. Since that outbreak, about 1,400 cases are officially reported to the Center for Disease Control annually.
Other bacteria and protozoa can also colonize water cooling system surfaces and some have been shown to promote legionella replication. Amoebae and other ciliated protozoa are natural hosts for legionella. Legionella multiply intracellularly within amoebae trophozoites. Legionella pneumophila is known to infect five different genera of amoebae, most notably Hartmanella vermiformis and Acanthamoeba. Legionella can also multiply within the ciliated protozoa, Tetrahymena. Bacterial species that appear to provide legionella with growth-promoting factors include Pseudomonas, Acinetobactor, Flavobacterium, and Alcaligenes. Copper and silver ions are an effective method of control for each of these bacteria and protozoa. The controlled release of copper or silver ions has also been known to serve as an effective attachment and growth control for such marine organisms as algae, mussels, oysters and barnacles. Such ions can eliminate and control algae, for example, by inhibiting photosynthesis which leads to its demise.
In the experience of these inventors, users of present metal ion generators in industrial cooling water systems have reported problems such as bridging which leads to electrical shorting, electrical conductivity stratification which results in uneven electrode erosion, and plating of metal on the cathode. Bridging occurs because of the necessity of placing the anode and cathode in close proximity to one another in fresh water systems. One way of dealing with this problem is to periodically reverse polarity of the electrodes. Uneven electrode erosion due to electrical conductivity stratification occurs for the reason that nonuniform water flow occurs between electrodes. In present designs, the velocity of the water that flows between the electrodes is not generally constant over the electrode face. This leads to stratification of inorganic materials in the water that, in turn, produces electrical conductivity stratification. Finally, plating of the metal anode material on the cathode, as previously mentioned, completely defeats the purpose of the ion generator in the present application. When plating occurs, the metal ions are deposited on the cathode rather than being introduced into flow stream that is to be treated. In the experience of these inventors, each of these problems is related to water flow and to electrode spacing, which is required to be very close in fresh water systems. The spacing of the electrodes in close proximity to each other in fresh water systems is required if power system expectations are to be within reason, on the order of a few hundred watts. The system simply will not be economical if maximum power requirements exceed several kilowatts.